This invention pertains to a thin-film head for producing, in a magnetic image-storage medium, a high-resolution, smooth-edge-defining dot-like magnetic image unit, and for reading the same. More particularly, it relates to the production of a somewhat doughnut-shaped magnetized region in such a medium, which region functions as a portion of a total magnetic image, with magnetization in the region characterized by multi-directionally oriented magnetic vectors distributed generally with spherical geometry, and with a magnetic field intensity which is significantly higher adjacent the perimeter of the region than in the central portion of the region.
The heads which are disclosed herein are structurally similar to that which is illustrated in FIGS. 5 and 6 in my U.S. Pat. No. 4,414,554, issued Nov. 8, 1983, for MAGNETIC IMAGING APPARATUS, and in the same two figures in my Belgium Pat. No. 891.603, issued Jan. 15, 1982 for MAGNETIC IMAGING METHOD AND APPARATUS. The disclosure of that prior U.S. patent is hereby incorporated by reference in the instant disclosure. The head of the present invention, in one special form shown herein, constitutes an improvement over the head disclosed in the just-referenced U.S. patent in its ability, when writing, to distribute flux over the central portion of a written image. FIGS. 1 and 2, described below, are substantially the same as FIGS. 5 and 6 just-above mentioned. FIG. 5 herein shows a unique hollow-head structure which is the special head form just referred to.
As discussed in my patent relative to a printing application, edge definition in a finally printed image is a key factor in achieving clarity in images such as alpha-numeric characters. Accordingly, a general object of the present invention is to provide a magnetic head having unique differential permeability characteristics which, when embodied in a geometric head structure like those disclosed herein and in my prior U.S. patent, contribute appreciably to enhanced edge definition in a finally printed image. Strong edge definition is also important in an image-reading operation.
According to the invention, the proposed thin-film head includes inner and outer, substantially co-planar, symmetrically arranged pole portions, with the inner pole portion having a magnetic permeability which is significantly lower (preferably by at least an order of magnitude) than that of the outer pole portion. In one embodiment disclosed herein, the head has an inner pole portion which includes a substantially full-circular exposed face, surrounded symmetrically by the outer pole portion which has a substantially annular exposed face. In another embodiment, both pole portions have substantially annular exposed faces.
With the magnetic permeabilities of the inner and outer pole portions related as just generally described, magnetic flux produced by the writing head to create a latent magnetic image unit in a recording medium is characterized by a density which is significantly higher at the perimeter of the image unit than in the central portion thereof. This situation results directly from the fact that the outer pole portion in the head, which defines the perimeter of the image unit, has a higher permeability, and thus tends to concentrate and densify magnetic flux.
A latent image unit created in a medium, with this kind of flux density characteristic, is extremely efficient in capturing printing toner, particularly around the edge of the unit. This situation serves to enhance finally printed edge definition in an image made up of a plurality of such units. Such an image, also, is very easily read.
A specially modified head which is shown herein has a hollow central pole. This kind of structure, when writing an image, allows central lines of flux to terminate on the inside of the tube-like wall in the central pole--resulting in a central flux distribution in a written image with strong vertical toner-capturing force vectors.
These and various other objects and advantages which are attained by the invention will become more fully apparent as the description which now follows is read in conjunction with the accompanying drawings.